Method of producing high vacuums in x-ray tubes and the like.



C. A. FRIEDRICH. METHOD 0F PRODUGING HIGH VAGUUMS 1N X-HAY TUBES AND THE LIKE.

APPLICATION FILED 00T. 11, 1910. BENI-WED MAY 2'?, 1913.

` 1939677 Patented Jan. 6, 1914.

IUNITED ESTATES PATENT OFFICE.

CHARLES A. FRIEDRICH, 0F NEW YORK, N.

METHOD 0F PRODUCING HIGH VACUUMS IN X-RAY TUBES AND THE LIKE.

Specication of Letters Patent.

Patented J an. 6, 1914.

Application led Oc'tler 11, 1910, Serial No. 586,443. Renewed My 27, 1913. Serial No. 770,259.

To 'all cvhom it may concern,

'Be 1t known that I, CHARLES A. FRIED- RICH, a citizen of the Empire of Germany,

and a resident of New York, county and' State of New York, have invented certain new and useful Improvements in Methods of ProducingV High -Vac'uums in v'X-Ray Tubes and the like, 'of which the vfollowing is a specification. f

This invention has reference to a novel method of producing high vacuums in X-ray tubes and the like and pertains also to inrproved tubes of that type.

The known X-ray and like tubes and the methods heretofore employed for producing high vacuums required in vsuch tubes are deficient. With the aid of the modern Roentgen apparatus it is possible to pass strong currents through the tubes but this involves certain disadvantages vand greatly shortens the life of the tube. Furthermore with the former X-ray tubes, X-rays may be produced of but moderate penetratlve power and more of the so called soft rays are produced than of the so called hard and penetrative rays because the inherent deficiencies of those tubes permit the passage vof the current between the anode and cathode only after the vacuum has been regulated down to a certain height. If 'this regulation is not effected the current docs not pass between the electrodes but discharges along the inner glass Walls of the tube and causes irregular fluorescence of the entire glass bulb without producing X-rays. If under those circumstances a stronger current is applied then the tube is usually destroyed because it simply cracks. These deficiencies of the former X-ray tubes iind their explanation in the method of their evacuation and lin the` disadvantageous location and construction of the regulating device.

In order to produce a lastingly high vacuum in an X-ray tube under present conditions when enormously strong currents are sent through .the tube during use both the anode and the cathode should be heated to red heat during the evacuation so that all gases contained in the metal are driven out and removed by the air pump. Thev regulating device sho'uld not be on the outside of the tube but should be located within same near the center so that the gases absorbed by the regulator may be easily liberated forthe purpose of forming a passage for the current.

The known methods of evacuation have the disadvantage that the same high potential current which produces the X-rays in the nished tube is also used for heating the electrodes during evacuation. The anode may thus be heated to red heat without causing disturbing secondary effects but not the cathode. The cathode acquires but little heat in a low vacuum and only after the cathodic rays become almost invisible it acquires heat quickly. If under those conditlons the current is not shut off, large quantities of gas are expelledfrom the cathodel while it acquires a red heat andthe current finds an easy Way through that gas layer and follows same. well as volatili'zed metal vapors are thrown against the glass Walls Where they form a precipitate in form. of a dark ring in the neighborhood of the cathode. A finished tube produced as described exhibits big disturbances around the cathode and such a tube is useless for practical purposes.

In the known methods of evacuation the cathode is not heated to red heat because it imperils the tube. As soon as the anode has acquired red heat the current is so reduced that the cathode will not be heated. For this reason current is passed interruptedly through the tube. A tube evacuated in the described manner still contains pretty large quantities of gas in lthe cathode and as the cathode easily acquires heat in a high vacuum these gases are set :tree during a continued use of the tube and the above described Aphenomena take place and the tube becomes useless in a very short time. l

Another disadvantage of the use of high potential currents during the process of evacuation is that even at a low vacuum an electrostatic eld exists in the tube which reduces to a large extent the efficiency of the air pump. As a consequence of this large quantities of gases which were expelled from the anode and cathode collect in the tube. By the continuous electric discharges and the static eld produced thereby these gases as well as volatilized metal vapors are thrown against the glass walls and settle thereon. When the nished tube becomes This causes that gases asV cold this fine deposit on the glass walls abfsorbs part of the gases still contained in the tube and thus forms a fine gaseous layer on vthe entire inner glass wall.A This explains Why the current in a completely cooled finished tube passes easier along the glass wall instead of passing between the anode. and cathode until the vacuum is regulated down.

In order to prove the existence of this fine gas layer on the inner glass wall reference may be made to a very simple method used years ago before regulating devices on X-ray tubes were known. When at that time a tube did not permit of the passage of the current between the anode and the cathode the tube was simply baked, that is, the tube was subjected to heat in a specially constructed oven. By this heat the gases absorbed by the deposit of metallic vapors on the glass Walls were set free and accordingly the vacuum 'in the interior of the tube was reduced. Care had to be taken that the tube was not appreciably cooled off before current was sent through same otherwise the loose gases would partially be reabsorbed by the metallic deposit on the glass wall and no current for practical purposes would pass. As above mentioned gases and volatilized metal vapor settled on the cooler glass wall and when a high vacuum was produced the static field within the tube prevented quick excavation as required for practical purposes. The pump appears not to be able to draw the residual liberated gases through said static field in a higher vacuum and for thisl purpose an external regulator has been used. Such regulator consists of prepared asbestos, isinglass, or chemicals possessing a high degree of absorbing gases. After the process of exhaustion the residual gases are absorbed by the deposit on the glass wall and particularly by the prepared mass in the regulator. As a consequence of this the vacuum in the center of the tube is practically a-n absolute one, in other words the passage of the current between the electrodes is opposed in such a high vacuum by a tremendous electric resistance. For this reason it is easier for the current to find its way heating of the regulator mass. Such regulator on a former tube contains asbestos prepared separately before the regulator was fused to the tube and during handling the regulator it reabsorbs some vapors and moisture. Further when fusing the regulator to the X-'ray tube water vapors are also formed from the blow pipe and the operator has to produce the former tubes.

whereby moremoisture 1s absorbed by the prepared asbestos-therein. This absorption too has the bad effect of requiring a much longer evacuation. The regulator being outside of the tube causes that the vacuum will be too high between the electrodes for the passage of the current which passage is limited to a certain vacuum. Thls must be established by means of the regulator before the current will ass between the electrodes. It is however esired to obtain rays of greater enetration, that is, rays which are in a still higher Vacuum than in I have produced a novel X-ray tube and devised a novel method of producing a high vacuum therein by means of which high heating of both electrodes in a relatively low vacuum is effected without the use of high potential currents whereby all the deficiencies of the former method, secondary disturbing phenomena are eliminated and the glass walls remain clear and free from deposits. Furthermore there is no static field which prevents the continuous uniform action of the vacuum pump which with the new method can scope easily with the liberating gases from the electrodes in an unobstructed manner. To avoid deposits of metal on the glass wall no high potential currents are passed through the tube during the process 0f evacuation and the absorbent mass of the regulator is located near the center of the vacuum so that the passage of the current is not opposed by an almost absolute vacuum. The new X-ray tube thus made produces rays of higher penetrative power than those heretofore made.

The peculiar construction of my electrodes renders it possible to heat both the anode and the cathode simultaneously to red heat by means of the common current used for incandescent lamps. The absence of electrical discharges and the static eld created thereby allows the pump to work with its full capacity whereby the liberating gases are quickly removed and cannot collect within the tube. Mercury vapors which formerly were produced within the evacuated space by the electrical discharges are accordingly not produced by my novel method and therefore not found in the nished tube.

Tov make the inventionl entirely clear reference is made to the accompanying drawing in which an X-ray tube is illustrated of my novel construction and exhausted according to my novel method and in which:

Figure l representsin elevation partly'in section an X-ray'tube embodying in desirable form the present improvements. Fig. 2 is a cross section on line 2 2 of Fig. l, and Fig. 3 is a modification.

In the drawing a represents the glass bulb,

v to the bulb by fusion.

b is a lon glass tube for the anodev integral with the ulb, c is a. somewhat wider and shorter lass tube for the cathode also integral with the bulb and d is-the remaining part ortip of the exhaust tube also sealed The anode passes through the long narrow tube b into the interior of the bulb and the cathode through the wider and shorter tube c. A terminal b1 is formed at the top end of the tube b clostube c which closes o' same hernietically.

There are also two auxiliary terminals e and f whose purpose will be explained farther down. s

The anode consists of a slotted steel tube g which has a longitudinal slot g1 that extends through its greater length. At the end of the slot g1 a lateral slot g2 is formed. The slots are provided in the steel tube to impart some spring power so that the tube lits into and bears against the inner walls of the Vglass tube b. To the top end portion of the steel tube a metal wire, 'preferably a copper wirev le, is soldered to which the platinum wire z' 'is fused which passes through the solid glass formed at t-he end of the tube and forms loutside the anode terminal b1. In the lower portion of the steel tube g there is the anode proper below the lateral slot g2. The anode j is 'made of metal such as bronze or copper in the usual manner and secured to the steel tube by means of a screw y'l. Below the securing screw 7'1 the steel tube is surrounded by an asbestos mantle which is held in position by a metal ring Z located on the bottom portion of the asbestos mantle and adapted to be tightened by a screw m' passing through two side flanges of the ring as shown in detail in Fig. 2. Around the asbestos mantle metal wire is wound preferably platinum wire n the one end of which is secured to the screw jl so that it is'in electric contact with the steel tube g and the terminal for the anode. The second end of this wire around the asbestos mantle is secured to a short screw o which ends on the asbestos and therefore is not. iii electric contact with they anode y'. As shown in Fig. 1 a conducting wire p leads from the tensioning screw lml to the auxiliary terminal e. In this way a circuitiiiay be established by mea-ns of the descent lamp current may be used for heating the high resistance wire n on the asbestos mantle and as may be seen from Fig. 1 both the asbestos mantle and the high resistance wire n are within the glass bulb near the center of the vacuum in the finished tube.

The cathode which is in the shorter and wider tube o opposite the anode consists of an aluminum rod g located in al narrow glass tube r. The bottom end of. the aluminum rod connects 4with the terminal c1 by means of a platinum wire s. The top end ofthe aluminum rod g is screwed into the cathode proper t. The cathode likewise is made of metal, cup shaped at the top and forms a thick rod t1;b,elow. The aluminum rod g is` preferably'` screwed into the rod portion t1 of the cathode while the glass tube r simply extends into an opening in the lower portion of the thick rod t1. The glass tube 1' is fused to the solid glass portion through which the platinum wire s passes. Around the thick rod portion t1 of the cathode t an asbestos mantle u is provided which is secured by means of a metal ring fr adapted to be tensioned in the same manner as the ring Z of theanode. High resistance or' platinum wire 'w is wound around the asbestos mantle whose top end is secured to a screw m and thus in electric Contact with the cathode. The bottom end of the platinum wire is secured by means of a short screw y to the copper ring u which screw ends on the asbestos mantle and therefore is not in electric contact with the cathode. In connection with the ring u is a small bar a which connects with the auxiliary terminal f. Thus a circuit may be established by ymeans, of the cathode termina-l c1 and the auxiliary terminal f of which the high resistance or platinum wire w forms part. In this manner the platinum wire fw may be heated by common street current or the incandescent light current.

` Assuming that the tube is in connection with the pump and is gradually exhausted then at a certain stage of the evacuation the platinum wire around the asbestos mantle is heated to incandescence. The asbestos niantle also gets hot and imparts heat to the anode below and after a certain time the anode proper acquires heat and becomes red.

'Simultaneously the cathode is heated in like manner. The gases contained in the metal of which the anode and cathode are made are gradually expelled and the liberating gases are at once removed by the air pump in an unobstructed manner because there is no stat-ic field within the tube. -As both electrodes areheated in this manner no gases will be expelled from the finished tube when a high potential current is passed through same. No deposit is formed on the inner glass walls ybecause there are no secondary disturbing phenomena within the tube under these conditions and there is no collec-tion of gasesas were retained in former tubes by the static field.

With the described construction` of the electrodes in the tube and the novel method. of evacuation a greatly improved tube is resulting whose glass walls remain clear from deposits. No gases can be expelled from the electrodes after the tube has been finished but over and above everything X- rays of. higher penetrative power may be produced with such tubes.

Then the finished tube made according to my novel method cools ott' the asbestos manlles naturally cool off too and as they are treated in the usual manner they absorb l the residual gases within the bulb whereby an almostabsolute vacuum is produced between the electrodes. If it is desired to use the tube current. is passed through the platinum wire on the asbestos mantles whereby some gases are expelled right in the interior -of the tube and almost in the path of the current. These expelled gases form so to say a conductive bridge for the high potential currents which then are passed through the electrodes proper.

ln order to render the regulating device automatic the size ot' the platinum wire on the asbestos mantles is so selected that the strength of the current of the Roentgen ap paratus is suliicient to heat that wire and thereby the asbestos mantles below same so that gases are expelled for the purpose of establishing a passage for the high potential current between the electrodes.

In Fig. 3 ot the drawing a modification of the described device for heating the electrodes by low potential currents is illustrated. In this modied form the high re-` sistance or platinum wire on the asbestos mantle forms a closed circuit in itselt1 and the heating of this wire and thereby the electrode is effected by induction from an outside primary spool of an induction coil C which fits over the glass tube L. The wire a then forms the tine wire of the induction coil and is heated when current is passed through the primary coil C. The platinum wire u.' on the asbestos mantle u of the cat-hode may likewise be heated by a suitable primary coil as described in connection with the platinum wire n on the asbestos mantle 7c of the anode.

l. claim :ny invention:

l. The method of producing a high vacuum in an X-ray tube which vacuum Will remain constant during a single operation consisting in heating to red heat both the anode and the cathode during evacuation by means oflow potential currents.

2. The method of producing a high vacuum in an X-ra-y tube which vacuum will remain constant during a'plurality of opera. tions consisting in heating to red heat both the anode and the cathode during evacuation by means ci low potential currents.

3. The method of producing a high vacuum in an X-ray tube which vacuum will remain comparatively permanent consisting in heatingl to red heat both the anode and the cathode during evacuation in a relatively low vacuum by means of 10W potential currents. Q

4. The method of producing a high vacuum in an X-ray tube which vacuum will remain comparatively permanent consisting in heating to a cherry red heat 4both the anode and the cathode during evacuation in a relatively low vacuum by means of low potential currents, and expelling thereby all gases contained in both the anode and the cathode.

5. The method of producing a high vacuum in an X-ray tube which vacuum will remain comparatively permanent consisting in heating to high heat both the anode and the cathode during evacuation in a relatively low vacuum, expelling thereby all gases 'from the anode and cathode, and removing said gases as they are set free.

6. The method of producing a high vacuum in an X-ray tube which vacuum will remain comparatively permanent consisting in heating a regulating device on each electrode within the tube near the center of the vacuum in an independent circuit by low potential currents during evacuation in a relatively low vacuum, and expelling thereby the gases from both the anode and cathode.

7. The method of producing a high vacuum in an X-ray tube which vacuumv will remain comparatively permanentI consisting in L heating a regulating device on each electrode within the tube in an independent circuit by loW potential currents in a relatively low vacuum, expelling thereby the gases from both the anode and cathode and removing same as lthey are set free.

8. The method of producing a high vacuum in an vX-ray tube which Vacuum will remain comparatively permanent and expelling gases lfrom regulators and both the anode and the cathode in one operation consisting in heating a regulator on'the anode and one on the cathode within the tube in a relatively low vacuum by means of low potential currents in an independent circuit, expelling thereby gases from the regulator and the anode and the cathode, removing said gases as they are set free until a high vacuum is obtained, allowing the sealed oft' tube to cool and the residual gases to be absorbed by the cool regulator.

9. The method of expelling gases from the cathode of an X-ray tube and the like during evacuation consisting in heating a regulating device on the cathode by means of low potential currents in an independent circuit in a low vacuum whereby the gases conta ined in the cathode are gradually expelled.

l0. The method of expelling gases simultaneously from both the anode and cathode of` anA X-ray tube and the like consisting in heating a regulating device on each of them by 10W otential currents in separate circuits Whlch are independent from the circuit of the electrodes, heating thereby gradually the anode and the cathode in a relatively low vacuum and expelling the gases 'contained therein and removing said gases.

l1. The method of evacuating and auto- \and a cathode, and an electric heater on the anode and one on the cathode Within the tube for the purpose of heating the anode and the cathode during manufacture.

13. An -X-ray tube comprising an anode and a cathode, an electrlc heater on the anode in an independent circuit, and an electric heater on the cathode in an independent circuit, both within the globe.

with central tubes thereon, an anode havlng an electric heater near its inner end within the globe, an auxiliary terminal for estab-' vlishing an independent circuit, al cathode with electric heater near its inner end, and

an auxiliary terminal for establishing an independent circuit.

15. An X-ray tube comprising a" globe I with central tubes thereon, an anode in one tube extending into the globe, a layer of asbestos lnear its inner end, high resistence wire thereon connecting with one end with the cathode and an auxiliary terminal connecting with the other end of said high resistance wire, a cathode, an asbestos, layer near its inner end, high resistance Wire on the asbestos connecting with one end with the cathode, an auxiliary terminal connecting with the other end of said high resistance wire'so that independent circuits may be established for the purpose of heating the anode `and cathode simultaneously but separately by low potential cugrents.

Signed at New York, N. Y., this 23rd day of September, 1910.

CHARLES A. FRIEDRICH. Witnesses;

CORINNE MYERS, THOMAS DONNELLAN. 

